Highly specialized organic polymers are used in many capacities as surface coatings in the manufacture of electronic devices. These polymer coatings may be permanent features of the finished product, but more often they are temporary coatings meant to serve as protective and/or sacrificial barriers. For example, in the manufacture of a logic device, a suitably reactive polymer, usually an electromagnetic radiation-reactive polymer may be used as a photoresist in a microlithography step to construct transistors or interconnects. Such polymers may also be referred to as photodefinable materials or as photoimageable materials.
In each instance in which the polymer is used as a protective or sacrificial coating, the polymer-coated surface is likely to be subjected to conditions so harsh that the nature of the polymer is profoundly changed, leaving ill-defined organic/inorganic surface residues. These residues must then be removed before the next step in the manufacturing process.
The polymer as initially applied may have been substantially soluble in many organic solvents. For instance, most photoresist polymers are designed to be soluble in such organic solvents as ethyl lactate, from which solution a thin layer of polymer is applied by spin-coating and solvent evaporation.
Thin polymer films applied by spin-coating solutions in organic solvents are easily removed by rinsing with the solvents used in the spin-coating process. The universe of solvents that may be used to remove spin-coated polymer films is not limited to the solvents used in the spin-coating process. For example, a thin film of a common Novolac-based photoresist, Megaposit™ SPR™220 from Dow Electronic Materials, applied by spin-coating an ethyl lactate solution, may be removed completely by rinsing with acetone or methanol from a solvent wash bottle.
However, after the polymer film has been subjected to a harsh processing step, such as a high-temperature bake, plasma etching or high-energy and/or high-dose ion implantation, the organic/inorganic material that remains is rarely soluble in any known organic solvent. For example, as is known in the art, polymers exposed to heat will cure to a higher extent due the formation of a surface skin, which results from accelerated curing from the heat, and higher bulk density at the surface. The polymer skin is more difficult to remove. As another example, high energy or high dose ion implantation can result in 3D crosslinking of the polymer, again resulting in much more difficulty in removal of the residue. In many cases, the only effective method of removing these residues consists of applying organic solvents that contain a strongly alkaline component. However, prior art compositions have been less than satisfactory for a variety of reasons.
Accordingly, a need remains for more effective cleaning agents to remove such difficult-to-remove residues.